1. Field of the Invention
The present invention relates to a method of polishing semiconductor wafers and other wafers made of quartz or a ceramic material (hereinafter referred to, for simplicity, as "wafers") while holding the wafers by a template instead of using an adhesive, so as to obtain polished wafers having an extremely high degree of flatness without involving declination caused by over-polishing at the respective peripheral portions of the wafers. The present invention also concerns a novel backing pad used in the polishing method, and a method of making such backing pad.
2. Description of the Prior Art
In the so-called "template" type polishing, a plurality of wafers are polished at one time while they are fitted in a plurality of circumferentially spaced engagement holes, respectively, with their backsides held by a backing pad. The template type polishing is generally achieved by an arrangement shown in FIG. 6, in which numeral 2 denotes a turn table, 4 a polishing pad, 6 a template blank having a plurality of engagement holes 8, 10 a backing pad, 12 a polishing plate, and 14 a polishing weight. As shown in FIG. 6, a plurality of wafers W (two being shown) are polished while they are fitted in the corresponding engagement holes 8 in the template blank 6. The template blank 6 and the backing pad 10 and the backing pad 10 and the polishing plate 12 are attached together by adhesive-bonding using an adhesive, so that they jointly constitute a jig T so-called "template" for mounting thereon wafers to be polished. In FIG. 6, the adhesive layers are omitted for purposes of illustration.
In the template type polishing described above, partly because the wafers W are plunged into the polishing pad 4 by the action of the polishing weight 14, and partly because the polishing plate 12 is bent or deflected toward the wafers W by the action of the polishing weight 14, a stress is concentrated on the peripheral portion of each of the wafers W. Due to this stress concentration, the polishing rate or speed is higher at the peripheral portion of each wafer W than at the central portion of the wafter W. Thus, the peripheral portion of the wafer W is polished away in a greater amount than the central portion, so that a finished wafer W is declined at its peripheral portion.
To avoid declination of the peripheral portion of the wafer W, the following measures have been taken.
(1) A rigid polishing pad 4 or a smaller polishing weight 14 is used to reduce the amount of sinkage or plunge of the wafer W in the polishing pad 4. This measure, however, brings about unfavorable effects, such as an increased amount of scratches and a reduction of productivity due to a reduction of polishing rate.
(2) A polishing plate 12 either made of a highrigidity ceramic material or alternatively having a greater thickness is used to reduce deflection or bending of the polishing plate 12. This measure requires an expensive material and hence is short of practical use.